We have a Trane Weathertron Xl1200 heating pump with the thermostat pictured below and are trying to replace it with our new Nest thermostat. Our old system has a variable speed air handler and we want to make sure that we hooked up the wiring correctly. We have electric heat with emergency backup. Is the wiring we have correct or do we need to change anything? We have the latest version of the Nest thermostat.

Old Thermostat Wiring Old Thermostat wiring

New Thermostat Wiring New Thermostat Wiring

  • Can you post photos of the wiring at the air handler end of your system, as well as the wiring diagram for your system? – ThreePhaseEel May 12 '19 at 15:41
  • Did you ever get this resolved? If so, please give a check-mark to the answer or write up your own answer explaining what you did to get it fixed and give yourself a check mark. That will help others with this kind of problem know that this has a resolution and is a good place to look for their answer. – FreeMan Aug 18 at 13:40

Here's the 1 Stage heat Pump with Aux heat and Emergency heat from the Nest Pro Installer Guide.

Your diagram is close, but Nest suggests to use Rc (it should internally jump Rc and Rh if necessary) and W -> W2/Aux.

1 Stage heat Pump with Aux heat and Emergency Heat

Note - variable speed fans are not supported, so proceed at risk.

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